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how to calculate non-window envelope gain/loss?

asked 2015-04-25 02:23:37 -0600

oat gravatar image

updated 2015-04-27 11:51:48 -0600

Is there a specific output variable(s) for building envelope (non-window surfaces) heat gain/loss?

Currently, I'm using the following way to indirectly estimate this quantity using an Ideal Loads Air System: non-window surface net heat gain = zone district cooling loads - zone infiltration net heat gain - zone internal heat gain (which includes heat gains from people, lights and equipment) - zone windows net heat gain

There are output variables for each of these items shown above, but I don't know if there is variable for heat gain and loss for each individual non-window surfaces or each thermal zone in EnergyPlus.

I ask this because I saw the following heating/cooling breakdown diagram on Autodesk webiste, and I wonder how the loads for walls and roof can be obtained ... link text

Can you kindly advise? Thanks!

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answered 2015-04-25 10:54:47 -0600

updated 2015-04-25 18:11:27 -0600

The available Output:Variables are listed in the .rdd file after a simulation. If you open this file in a text editor and search for "heat gain" you'll find the variables that make up the envelope load broken down into conduction, convection, and radiation for inside and outside surfaces. If you're using the IDF Editor, the list of available Output:Variables will also be available in a dropdown field after simulation.

There's also a Standard Report for Sensible Heat Gain Summary in the .html file that lists the Annual Building Sensible Heat Gain Components by zone. However, this appears to give the net heat transfer on an annual basis, i.e. no heat gain only heat loss in a heating dominated climate/building.

Example of Available Outputs from RDD File

Output:Variable,*,Surface Inside Face Conduction Heat Transfer Rate,hourly; !- Zone Average [W]
Output:Variable,*,Surface Inside Face Conduction Heat Gain Rate,hourly; !- Zone Average [W]
Output:Variable,*,Surface Inside Face Conduction Heat Loss Rate,hourly; !- Zone Average [W]
Output:Variable,*,Surface Inside Face Conduction Heat Transfer Rate per Area,hourly; !- Zone Average [W/m2]
Output:Variable,*,Surface Inside Face Conduction Heat Transfer Energy,hourly; !- Zone Sum [J]
Output:Variable,*,Surface Outside Face Conduction Heat Transfer Rate,hourly; !- Zone Average [W]
Output:Variable,*,Surface Outside Face Conduction Heat Gain Rate,hourly; !- Zone Average [W]
Output:Variable,*,Surface Outside Face Conduction Heat Loss Rate,hourly; !- Zone Average [W]
Output:Variable,*,Surface Outside Face Conduction Heat Transfer Rate per Area,hourly; !- Zone Average [W/m2]
Output:Variable,*,Surface Outside Face Conduction Heat Transfer Energy,hourly; !- Zone Sum [J]
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Thank you, Matthew!

Can you kindly advise on how to summarize these surface related output variables to get the net heat gain/loss value for a given surface?

E.g. is it like the following?

net heat gain for outside face = convection gain + conduction gain + radiation gain

net heat gain for inside face = convection gain + conduction gain + radiation gain

net surface gain = net heat gain for outside face - net heat gain for inside face

......

oat gravatar image oat  ( 2015-04-27 11:56:39 -0600 )edit

HI did the following work for net surface gain results?

Pavithra.Lakshmi gravatar image Pavithra.Lakshmi  ( 2017-10-28 19:23:06 -0600 )edit

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Asked: 2015-04-25 02:23:37 -0600

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Last updated: Apr 27 '15